Thermal control for electric circuit



April' 29, 1943. R. R; KERNEN THERMAL CONTROL FOR ELECTRIC CIRCUITS Filed April 10, 1941 if .71? Kerzzezz Patented Apr. 20, 1943 THERMAL CONTROL FOR ELECTRIC CIRCUIT 10 Claims.

This invention is concerned with improvements in thermal regulators for an electric circuit, and particularly with a regulator that effectively opens the electric circuit on failure of heat supply to the regulator.

This invention may be illustrated by reference to a pilot control for gas or oil burners. Such pilots of various sorts are known of .themselves. For example. a pilot flame is maintained at the fuel burner to assure ignition of the issuing fuel. In conjunction with the burner are auxiliary devices driven by electricity, such for example as pumps to supply the fuel. Air or water pumps are similar auxiliary electric equipment that may cooperate with a pilot flame. Not all such auxiliary devices are pumps, but may be valves as for example in a gas line for domestic burners. Sometimes the pilot flame becomes extinguished and sometimes the fuel fails to ignite, yet the fuel supply may continue. With continued supply of fuel under such circumstances the result is not only wastage of fuel but may involve considerable fire hazard by accumulation of unburned fuel. This is so especially with gas fired furnaces. It is desirable to provide control apparatus that is responsive to failure of a pilot heater.

Under this invention a particular purpose is to regulate an electric circuit so as to open the circuit when a pilot heater fails. A further purpose is to regulate an electric circuit associated with 1 a burner so that the current may diminish when a pilot flame burns low and may increase when the pilot burns high in a range of temperature below which current ceases.

fuel in correlation to the greater or less intensity of a pilot flame. This invention provides regulation of auxiliary electrical devices while a pilot flame is burning as well as providing a cut-off for the circuit when the pilot. ceases burning.

A general purpose is to open and to close an electric circuit in accordance with a supply or diminution of heat applied to the circuit above certain critical temperatures.

A further purpose of this invention is to arrange an electric circuit control unit that can be removed readily from a position and that can be renewed eas ly if need be.

This invention will be illustrated by a. specific embodiment shown in the accompanying drawing, and novel features of the invention will be pointed out more particularly in the appended claims.

' In the drawing:

This arrangement therefore could supply greater or less amounts of Figure I shows in cross section a specific, removable control unit; and

Figure 2 illustrates diagrammatically a system of control of a gas burner, involving an electric circuit in which is included the thermal control of this invention.

According to this invention various benefits result from a control unit comprising two electric conductors separated by a composition that is non-conducting in the solid state but becomes conducting when fused. Preferably such intermediate material is distributed through an inert non-conducting base. In a specific form, such thermal control for an electric circuit is formed as a replaceable unit anrl comprises a casing of metal adapted to serve as one electrode, with a core of porous non-conducting base in which is a fusible compound of the sort described. for example sodium tetraborate, with a central bore containing an inner electrode.

This invention will be clarified by description of the specific embodiment illustrated in the drawing, though the invention may be practiced otherwise than thus specifically.

Referring to the drawing, Figure 1 shows in cross section a cylinder adapted to be used as a replaceable plug 1 in an electric system The cylinder comprises an outer wall 2 of metal. This outer wall of metal may be provided with means to dissipate heat, such for example as a collar 2' at the inner end of the plug. The collar end is shown as being threaded to facilitate insertion in suitable electric socket. If desired, auxiliary radiating fins or corrugations or other means of promoting dissipation of heat may be applied to the outer metal casing 2 of the control plug. In the form shown in the drawing, the outer casing 2 is filled compactly with a separable cylinder 8 of non-conducting material. Suitable material is inert under temperatures to be encountered. For example, fused aluminum oxide bonded ceramically constitutes a suitable inert base. Alternatively instead of being bonded ceramically the aluminum oxide may be compressed suificiently to be coherent and strong enough for the present purpose.

This filler in any event is in fact sufliciently porous to contain fusible composition 5. However other openings than pores strictly may be provided to contain the fusible composition. A suitable composition 5 that will fiow readily into the pores of carrier 4 is sodium tetraborate. This exemplifies material that will fuse when heat is applied, that when fused is an electrical conductor but that when solid is non-conducting.

. known of itself closes the main burner.

' the gas flame is removed or At lower temperatures sodium tetraborate solidi- .fies, probably forming super-cooled solid solutions, and when so cooled the tetraborate is nonconducting. In the fused state. ions are produced that transmit electric current. The line of demarcation between fused solution and solid is rather sharp so as to act as a control to open an electric circuit rather quickly. When the circuit is closed however increase in temperature increases the ionic conduction and thus promotes flow of electricity. This flow of electricity of course is between an inner electrode 3 and outer electrode 2. The interior of the carrier base 4 is bored to receive electrode 3 as a rod. Thus each of the elements of this plug is removable and replaceable; namely, outer metal cylinder 2, inner core a and inner electrode 3. In the drawing, both electrodes are shown threaded to facilitate insertion in an electric circuit, but it is evident that other arrangements for this purpose may be applied.

In Figure 2, thermal control plug i is shown in combination with a pilot burner in a gas burner system. The control plug i is shown as part of an electric circuit 6 that operates a valve I to regulate the supply of gas to a main burner 8. In this system a branch gas line 9 supplies fuel to a pilot Ill. The burner i is positioned under projecting control tube I. Thus when the pilot flame fails, current ceases to flow in the electric circuit and this by suitable mechanism well supply of gas to the When the gas flame is burning, current flows through the electric system so as to maintain the gas supply valve in some open position.

In the plug illustrated in Figure 1, the porosity of the inner carrier base 4 promotes quick action of the control both in opening and in closing the electric circuit. Thus the sodium tetraborate because of its distribution extensively over the surfaces of the pores of the base is in relatively thin films and thus capable of cooling quickly or of being heated quickly and uniformly. However, because of the extensiveness of a porous system the total amount-of conducting fused salt may be relatively considerable. In cooling, when is extinguished dissipation of heat from plug I is promoted by the extensive surfaces of the outer metal casing 2. This heat loss may be accelerated by the collar 2' at the base of plug I or by such other heat-dissipating devices as those skilled in the art will now be led to devise. The inner electrode also promotes extraction of heat from the core carrier, particularly in view of the relative thinness of wall of this hollow plug form of controlling unit.

Sodium tetraborate is preferred as the ionlzable fusible composition to be distributed between the electrodes. It ionizes adequately at approximatelyv 750 C. and operates satisfactorily in a temperature range of about;v 750 C. to 1000 C. This is suitable for domestic burners. Nevertheless other substances that exhibit similar properties may be used. For example, potassium metaborate will be suitable, as .well as sodium metaborate. Potassium aluminum silicate would be suitable though this substance is not stable .above 1100 C. Compounds that contain considerable relative proportions of acid anhydride such as sodium tetraborate and sodium pyrophosphate are fused. This means quicker action and greater sensitivity of the thermal control plug. Further.

a desirable quality in vention is the ability to compositions for this inform a super-cooled solid reasonably sharp the other hand quickly when the falls.

In this description cease range of temperature, or on s to become conducting temperature of the control unit a pilot burner has been mentioned for heating the control unit, but other borates such as of potas complex borates than of heating may be which a sharp temperature cut-oil is For example in the form of control unit sium for example or other tetraborate; and

similarly complex or mixed borates.

While in accordance with the patent statutes.

I have described a preferred embodiment of this and non-conducting when solidified.

3. A thermal controller :omprising a plug adapted to be secured in a :ircuit comprising a metal sheathing to serve is one electrode and containing a porous filler n fused aluminum oxide with sodium tetraborate distributed throughout the porous filler, and a second electrode contained in the filler for electrical contact with the first electrode on fusing with the tetraborate, the metal sheating comprising means to dissipate heat from the tetraborate.

8. A thermal controller for an electric circuit comprising conducting elements spaced apart by an inert porous insulator, the pores of which contain a fusible composition capable of becoming electrically conducting when fused and non-conducting when solidified.

ROBERT R. 92m, NEN. 

